Evidences have been published that the particular composition of the bank vole PrPC, not only renders bank voles highly susceptible to most of all known prion strains [7, 44, 54, 62, 75], but it is also responsible for generating a spontaneous and transmissible prion disease when expressed in a transgenic mouse model [17, 29, 56, 57, 76]. This evidence concerns the gene PRNP and prion disease.